Microbiology of diabetic foot osteomyelitis – Is it geographically variable?

•Diabetic foot osteomyelitis is difficult to diagnose and treat. Microbial pattern and their resistance can vary geographically.•Concordance rate of organisms was 66% when both bone culture and deep soft-tissue culture grew organisms.•Polymicrobial infections were seen in a very small proportion (about 5%). After Staphylococcus, Pseudomonas was second common organism that grew in cultures.•This is the first study detailing the microbial pattern of diabetic foot osteomyelitis using deep tissue culture and comparing with bone culture from India. Diabetic foot osteomyelitis (DFO) is a dreaded complication as both diagnosis and treatment of the condition is laborious. However, for proper decision on antibiotics in medical management of DFO, accurate determination of microbes is necessary to narrow the spectrum of coverage and to reduce adverse effects of long-term administration of antibiotics. With differing pattern of use of antimicrobials and their resistance pattern in different countries, it is empirical to determine the microbiological characteristics of bone cultures in DFO from a referral institute in South India. This study was a retrospective chart review of all cases of proven DFO who had consented for debridement and bone culture or those who underwent amputation. Both deep soft tissue (DST) and bone cultures were obtained for aerobic bacteria. Clinical characteristics and site(s) of DFO were recorded. Investigations for peripheral artery disease were performed if clinically indicated. In all, 105 patients with DFO were reviewed. Mean age was 62 years and 70% were men. Of those who were screened, 57% had evidence of peripheral arterial disease by arterial doppler. 46% of bone culture samples were sterile. Gram- negative organisms were more common (58%). Following staphylococcus, pseudomonas was the second common isolate. Of total staphylococcal isolates 37% were MRSA and 33% of klebsiella isolates were ESBL producing. Concordance rate between DST and bone cultures was 66%. 90% were mono-bacterial isolates. The commonest site of involvement of DFO was terminal phalanges of toes rather than base of 1st metatarsal. Widespread use of antibiotics, tropical climate and route of entry of organisms causing DFO differed in our cohort of patients. Further studies from different regions of world would shed light onto different pattern of microbes causing DFO.